Ought to Be and Ought to Do: Study of James Forrester's View on An Important Distinction in Deontic Logic

Ranjbari, Fereshteh; Nabati, Fereshte

doi:10.30465/lsj.2026.52892.1506

Ought to Be and Ought to Do: Study of James Forrester's View on An Important Distinction in Deontic Logic

Document Type : Review

Authors

Fereshteh Ranjbari ¹

Fereshte Nabati ²

¹ Department of Philosophy and Logic, Humanities Faculty, Tarbiat Modares University, Tehran, Iran

² Department of Philosophy, Faculty of Humanities, Allameh Tabataba'i University, Tehran, Iran

10.30465/lsj.2026.52892.1506

Abstract

Standard deontic logic is unable to distinguish between arguments that contain ought-to-be and those that contain ought-to-do, using the same formalization for both. Yet these two types of “ought” are semantically and logically different, and a logician who works with Standard deontic logic cannot separate them. Ignoring this important distinction creates serious problems, most notably the neglect of the role of the agent in moral action. In this paper, we demonstrate that drawing inferences from one type of “ought” to the other is not valid, and that the only relation that may be drawn between them is an empirical one rather than a logical one. Finally, we examine NDL deontic logic, which is introduced by James Forrester as a solution to this problem, and show that although it resolves some of the shortcomings of Standard deontic logic, it has not succeeded in preserving its neutrality with respect to ethical theories.

Keywords

Deontic logic

Standard deontic logic

Ought to be

Ought to do

Subjects